1. Field of the Invention
The invention relates to the use of microwave hybrid junctions as phase modulating and switching devices.
2. Description of the Prior Art
Hybrid junctions are a common type of directional coupler used in microwave systems today. The hybrid junction as used herein is a 4 terminal pair device which ideally has the property that power supplied to a given terminal is divided between two of the 3 remaining terminal pairs with nothing coupled to the 4th terminal pair. One of the most common classes of microwave hybrid junctions is a 3 DB directional coupler known as the phase quadrature type. The phase quadrature junction is usually two lengths of wave guide positioned in parallel and having a common wall. A symmetrical coupling element between the two lengths of wave guide usually takes the form of a slot in the common wall. A second well known class of hybrid junction is best known by the designation magic tee. The magic tee is an E and H plane tee junction having a first pair of symmetrical arms, which may be colinear, an H-plane arm and an E-plane arm. The H-plane and E-plane arms are connected to the colinear arms at their midpoint to form the junction.
H. Seidel, in U.S. Pat. No. 3,559,108, describes 3 DB coupler switches in which one pair of conjugate terminals is terminated with switchable impedances. Seidel describes the use of quadrature couplers and magic tee couplers as switches with high attenuation in the open state and bandpass characteristics in the closed state. U.S. Pat. No. 3,500,259 also to Seidel, is a related patent describing the use of hybrids with switchable terminations as filter circuits. U.S. Pat. No. 3,931,599 of Edward Salzberg (the present inventor) describes a phase inverter using hybrid junctions in which terminals terminated with switchable impedances are always controlled to have opposite impedance conditions. Seidel was primarily interested in filters and apparently did not recognize the possibilities of broadband phase switching. The tee type phase inverter of Salzberg did not stay well matched unless the terminating impedances were always in opposite states.